Which compound is known as oil of winter green?

Among the following compounds,the most acidic is

Compound$(s)$ which will liberate carbon dioxide with sodium bicarbonate solution is/are:
$A = \text{2,4,6-triamino phenol}$
$B = \text{Benzoic acid}$
$C = \text{Picric acid (2,4,6-trinitrophenol)}$

$X \xrightarrow{PCl_5} C_2 H_5 Cl$
$Y \xrightarrow{PCl_5} CH_3 COCl$
$X$ and $Y$ are:

When ethane-$1, 2$-dioic acid is heated with conc. $H_2SO_4$,it gives

An acyl halide is formed when $PCl_5$ reacts with an